Acoustic airflow estimation from tracheal sound power

Acoustical analysis of the respiratory sounds (tracheal and lung sounds) has been used to detect respiratory phases (inspiration/expiration) without airflow measurement . This technique facilitates the estimation of airflow by locating the zero crossing of phase transitions from respiratory sounds. Using statistical analysis, previous studies have shown that there is a relationship between respiratory sounds and airflow. However, no attempt was made to estimate airflow and evaluate the error. Therefore, the purpose of this study was to determine the best model for airflow estimation by acoustical means. Based on some preliminary studies, an exponential model was used to estimate respiratory airflow from average power of tracheal sounds. The model needs only a few breath sounds recorded with airflow for calibration for each subject. The model parameters were derived from the breaths with known airflow and then applied to the rest of the breath sounds to estimate airflow. The model was tested by estimating airflow at various rates from tracheal sounds of ten healthy subjects. Since relationship between airflow and average power of tracheal sound was found to be different for inspiration and expiration, therefore the model parameters were derived for each phase separately. Estimated airflow was compared to actual recorded airflow to determine the error. The results showed that the estimated airflow followed actual airflow well with an error of 5.8 ± 3.0% of the target airflow.